JP3001363B2 - Method of forming metal spray coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a boiler tube, a pipe in a furnace, a heat exchanger, and the like on the outer surface of a metal strip.
The present invention relates to a method for forming a metal film having corrosion resistance and wear resistance by thermal spraying.

Conventionally, in order to impart corrosion resistance and wear resistance to the outer surface of a metal strip used for boiler tubes, furnace piping, heat exchangers, etc., a self-fluxing alloy is sprayed on the outer surface, and then the gas is sprayed. A powder layer is formed by performing remelting treatment by heating or the like, or spraying cermet or ceramic.

[0003] However, since pores are formed in the ceramic, when smoothness is required, a process such as sealing the sprayed surface must be performed.
Met is not only expensive and has poor spraying work efficiency, but also
There is a problem that it is not suitable for forming a thick film.

[0004] Spraying a self-fluxing alloy has been considered because of the above-mentioned problems in thermal spray coatings such as cermets and ceramics. Although this self-fluxing alloy is inexpensive and has good performance after construction, it has been found that when the long material is re-melted by gas heating, the work efficiency is poor and there is a problem in quality stability.

[0005] Therefore, it has been considered that a self-fluxing metal is sprayed to form a sprayed film and then re-melted by high-frequency induction heating. Certainly, high-frequency induction heating is suitable for remelting long materials, but if the remelting process is performed in the atmosphere, it is performed in an oxidizing atmosphere. The surface of the film becomes rough. This rough surface is no problem if the surface is polished. However, in the case of a boiler tube which is often used in a state of being re-melted, the problem due to the rough surface remains at a later date.

When the base material is a low-alloy steel or an austenitic stainless steel, if high-frequency induction heating is performed during the re-melting process, the properties of the base material change before and after the process, and after the re-melting process, the sprayed coating is cracked. Therefore, it is necessary to adjust the cooling rate after heating so that the properties of the base material do not change.

[0007]

SUMMARY OF THE INVENTION In view of the above-mentioned prior art, the present invention forms a metal sprayed coating having good corrosion resistance and wear resistance on the outer surface of a metal strip without impairing the properties of the base material. It is an object of the present invention to provide a method for performing such operations.

[0008]

SUMMARY OF THE INVENTION The present invention has been made for the purpose of solving the above-mentioned problems, and has a configuration in which a self-fluxing alloy is sprayed on the outer surface of a metal strip to form a coating, and then the coating is formed. It is characterized in that a chemical containing borax as a heat-resistant antioxidant is applied to the sprayed coating in the form of a solution, dried, and then re-melted by high-frequency induction heating.

According to the present invention, when re-melting by high-frequency induction heating, a heat-resistant antioxidant having a high melting point, such as a flux, is previously placed on a sprayed film of a self-fluxing alloy formed on the outer surface of a metal strip. Is applied, even if re-melting treatment is performed by high-frequency induction heating in the air, a good quality metal sprayed coating can be formed without causing surface roughness on the surface of the coating.

[0010] Further, when a metal strip having a sprayed coating of a self-fluxing alloy formed on its outer surface is difficult to apply an antioxidant on the sprayed coating, or when the metal strip is a long material, the thermal spraying is performed. If re-melting treatment is performed by high-frequency induction heating while flowing an inert gas through the coating portion, a high-quality metal spray coating can be formed without causing roughening of the coating surface.

Further, when the metal strip is a low-alloy steel pipe, the sprayed coating formed on the outer surface of the steel pipe is subjected to re-melting treatment by high-frequency induction heating. By cooling to a certain temperature, the base material begins to transform, and is covered with a heat insulating material before the temperature does not become torstite or bainite structure, and gradually cooled,
The structure of the steel pipe becomes the same as the structure before the treatment, the hardness does not change, and the occurrence of cracks in the coating after the remelting treatment can be prevented.

On the other hand, when the metal strip is a long austenitic stainless steel pipe, if cooling is performed normally in the cooling process after re-melting heating, sensitization occurs. By moving and heating the inner surface while flowing cooling air to increase the cooling rate, sensitization can be prevented and a high quality metal spray coating can be formed.

[0013]

Next, an embodiment of the method of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of a main part in an embodiment of the method of the present invention, FIG. 2 is a cross-sectional view of a main part in another embodiment of the present invention, and FIG. FIG. 4 is a cross-sectional view of a main part of another embodiment of the present invention, in which another embodiment of the present invention is implemented.

In FIG. 1, reference numeral 1 denotes a steel pipe on which a metal spray coating is to be formed, 2 denotes a spray coating formed by spraying a self-fluxing alloy on the outer surface of the steel pipe 1, and 3 denotes a flux applied to the outer surface of the spray coating 2. An antioxidant layer C made of a material is an annular high-frequency inductor. After spraying a self-fluxing alloy on the outer surface of the steel pipe 1 to form a sprayed film 2, a flux material is applied to the outer surface of the sprayed film 2. After the antioxidant layer 3 is formed, the steel tube 1 is passed through the high-frequency inductor C, and the sprayed coating 2 is re-melted by induction heating with the high-frequency inductor C while relatively moving both. By doing so, the thermal spray coating 2 is re-melted without roughening due to oxidation, and a good quality metal thermal spray coating is formed.

FIG. 2 shows that a heat-resistant glass tube 4 is disposed outside the steel tube 1 on which the thermal spray coating 2 is formed, and the glass tube 4 surrounds the vicinity of the re-melting heating section, and the gas supply provided in the glass tube 4. A state in which an inert gas is continuously fed into the glass tube 4 from the inlet 5 and the sprayed coating 2 is re-melted by induction heating by the high-frequency inductor C while spraying the sprayed coating 2 from the tip side. And by doing this,
The thermal spray coating 2 is subjected to the remelting treatment without causing the rough surface due to oxidation, and a high quality metal thermal spray coating is formed.

FIG. 3 shows a state in which the thermal spray coating 2 formed on the outer surface of the low alloy steel pipe 11 is subjected to re-melting treatment. In FIG. 3, reference numeral 6 denotes a thermal spray coating subjected to re-melting treatment, and 7 denotes an outer surface of the thermal spray coating 6. A high-frequency induction heating method according to the method of FIG. 1 or 2, and then cooled to a temperature at which the re-melted thermal spray coating 2 becomes a stable thermal spray coating 6; -Cover with a heat insulating material 7 before the temperature at which the structure does not become a tightness or a bainite structure, and gradually cool. By doing so, the structure of the low-alloy steel pipe 11 becomes the same as the structure before the remelting treatment, the hardness does not change, and it is possible to prevent the coating 6 after the remelting treatment from cracking.

FIG. 4 shows an austenitic stainless steel pipe.
12 shows a state in which the thermal spray coating 2 formed on the outer surface of 12 is subjected to a re-melting treatment. In the figure, reference numeral 8 denotes a dummy tube, 8a denotes a mounting table thereof, and 9 denotes a compressed air inlet provided in the dummy tube 8. In the re-melting process according to the method shown in FIG. 1 or FIG. 2, while the compressed air is being sent from the compressed air inlet 9 into the steel pipe 12 through the dummy pipe 8 and cooled, the high-frequency inductor C is moved and heated to re-melt. It does the processing. That is, by cooling the re-melted and heated steel pipe 12 from the inner surface, the cooling rate is increased, and particularly between 500 and 800 ° C. Generally, when austenitic stainless steel is slowly cooled to between 500 and 800 ° C., Cr carbides precipitate at grain boundaries and become sensitized, deteriorating the inherent corrosion resistance and mechanical properties of stainless steel. According to the method of the present invention,
Precipitation of carbides can be prevented, and the characteristics of austenitic stainless steel can be maintained.

In the above embodiment, a method of forming a metal spray coating on a steel pipe has been described. However, the present invention is not limited to a steel pipe, and may be applied to a case where a metal spray coating is formed on another metal strip. Of course, it is applied.

Next, a working example in which a metal spray coating is formed by the method of the present invention will be described. Application example 1 Metal pipe-steel pipe Material STPA 22 Dimension φ48.8 × 5.1t × 3000L Composition C = 0.09 Mn = 0.55 Cr = 1.10 M = 0.55 Metal powder Type MSFNi-4 (Ni-based self-fluxing alloy) Thermal spraying (gas flame spraying) ) Conditions Rotational speed 300rpm Oxygen 25 psi Acetylene 15 psi Discharge rate 20 Lbs / Hr Surface treatment (flux coating) Type Borax alcohol solution High frequency induction heating Condition Heating temperature 10210-1080 ° C Cooling condition Heating air cooling (natural) When the metal sprayed coating was formed on the outer surface of the steel pipe under the above conditions, the surface roughness of the coating surface was Ra 2.0 μm, which was remarkably improved compared to the untreated surface roughness Ra of 20 μm. In observation of the cross section of the film, no abnormality was observed in the pores, hardness, etc., and good results were obtained.

Application Example 2 Metal tube-steel tube Material STPA 22 Dimension φ48.8 × 5.1t × 3000L Composition C = 0.09 Mn = 0.55 Cr = 1.10 M = 0.55 Metal powder Type NSFNi-4 (Ni base self-fluxing alloy) Gas flame spraying) Conditions Rotation speed 300 rpm Oxygen 25 psi Acetylene 25 psi Discharge rate 20 Lbs / Hr Thermal spray coating 1.5 mm Inert gas seal Glass container Quartz glass φ60 × 40
0L Atmosphere gas Argon High frequency induction heating condition Heating temperature 10210 to 1080 ° C Cooling condition Air cooling after passing through inert gas seal Under the above conditions, a metal sprayed coating was formed on the outer surface of the steel pipe. Been formed.

Application Example 3 Metal pipe-steel pipe Material STPA 24 Dimension φ48.8 × 5.1t × 3000L Composition C = 0.12 Mn = 0.55 Cr = 2.15 M = 1.00 Metal powder Type MSFNi-4 (Ni-based self-fluxing alloy) Thermal spraying ( Gas flame spraying) Conditions Rotational speed 300 rpm Oxygen 25 psi Acetylene 15 psi Discharge rate 20 Lbs / Hr Thermal spray coating 1.5 mm Surface treatment (flux coating) Type Borax alcohol solution High frequency induction heating Condition Heating temperature 1021-1080 ° C Cooling condition Approximately 200 ° C with 50mm thick insulation from 900 ° C after heating
When a metal spray coating was formed on the outer surface of the steel pipe under the above conditions, no cracks were found in the coating layer. In addition, the results of observation of the film surface roughness and cross section were as good as in Working Example 1, and no martensite or bainite transformation was observed from the results of the measurement of the structure and hardness of the base material.

Application Example 4 Metal tube-steel tube Material SUS 304 TB Dimension φ48.6 × 5.0t × 3000L Composition C = 0.05 Mn = 1.10 Ni = 10.00 Cr = 18.50 Metal powder Type MSFNi-4 (Ni-based self-fluxing alloy) Thermal spraying (Gas flame spraying) Conditions Rotation speed 300 rpm Oxygen 25 psi Acetylene 15 psi Discharge rate 20 Lbs / Hr Sprayed film 1.5 mm Surface treatment (flux coating) Type Borax alcohol solution High frequency induction heating Condition Heating temperature 10210 to 1080 ° C Cooling Conditions Air cooling of 5 kgf / cm ² is applied to the inner surface of the tube. When a metal spray coating was formed on the outer surface of the steel pipe under the above conditions, no crack was observed in the coating layer. In addition, the results of observation of the film surface roughness and cross-section were as good as in Working Example 1, and no microstructure was observed from the microscopic observation of the base material.

[0023]

The present invention is as described above. After spraying a self-fluxing alloy on the outer surface of a metal strip to form a film, the sprayed film is coated with a chemical containing borax as an antioxidant in a solution. The re-melting treatment is performed by high-frequency induction heating while applying in the form of an oxidizing atmosphere or reducing the oxidizing atmosphere with an inert gas.This prevents the surface of the thermal sprayed coating from being oxidized and roughening the surface. A thermal spray coating can be formed, and when the base material of the metal strip is a low alloy steel or an austenitic stainless steel, a good quality metal spray coating can be formed by adjusting the cooling process.

Therefore, the present invention provides a method for manufacturing a boiler tube, a furnace pipe, a heat exchanger, and the like on the outer surface of a metal strip material.
It is suitable as a method for forming a metal film having corrosion resistance and wear resistance by thermal spraying.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part in a state where an example of the method of the present invention is performed.

FIG. 2 is a cross-sectional view of a main part in a state where another example of the present invention is implemented.

FIG. 3 is a cross-sectional view of a main part of another embodiment of the present invention.

FIG. 4 is a cross-sectional view of a main part in a state in which still another example of the present invention is implemented.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steel pipe 11 Low alloy steel pipe 12 Austenitic stainless steel pipe 2 Thermal spray coating 3 Antioxidant layer 4 Glass pipe 5 Gas inlet 6 Resprayed thermal spray coating 7 Insulation material 8 Dummy pipe 8a Dummy pipe installation table 9 Compressed air inlet

Claims (4)

(57) [Claims] After coating a self-fluxing alloy on the outer surface of a metal strip material to form a film, a chemical containing borax as a heat-resistant antioxidant is applied to the sprayed film in the form of a solution and dried. And then re-melting by high frequency induction heating. 2. The method according to claim 1, wherein the oxidizing atmosphere is reduced during the remelting heating by continuously flowing an inert gas through the sprayed coating to be treated during the remelting treatment by high-frequency induction heating. 3. When the base metal component of the metal strip is alloy steel, and the structure of the base metal changes and transforms due to cooling after re-melting treatment by high-frequency induction heating,
When the film is at the film surface temperature where it solidifies and cools down by cooling,
That is, the method according to claim 1 or 2, wherein the coating is coated with a heat insulating material before the start of transformation. 4. When the metal strip is an austenitic stainless steel pipe, high-frequency moving heating is performed while flowing cooling air through the steel pipe to prevent sensitization during the cooling process after the re-melting process. The method according to claim 1.